SSC01-VIIIb-1 The PCsat Mission and Cubesat Design Notes Bob Bruninga, WB4APR, ENS Boutros, ENS Nolan, ENS Schwenzer, ENS Lawrence, LTCL B. Smith, Dr. D. Boden US Naval Academy Satellite Lab 590 Holloway Rd, Annapolis, MD 21402 [email protected] 410-293-6417 FAX 410-239-2591 Abstract There are growing opportunities for Universities to gain educational access to Space. The Naval Academy has used the Department of Defense Space Test Program for its PCsat and Sapphire projects and the Stanford Cubesat program offers a unique opportunity to get numerous small student satellite payloads into space. As a spin-off of our PCsat project, we have investigated several off-the-shelf solutions to the Telemetry, Command and control portion of small satellites that can greatly simplify small satellite and CubeSat designs. This permits students to concentrate on the various payloads and other aspects of the project without starting from scratch with a comm. system. This simple comm. System based on AX.25 packet radio is being flown this summer in the Naval Academy’s Personal Communications Satellite (PCsat) which will demonstrate downlinks receivable on Hand Held Transceivers (HT’s) with only a whip antenna. Further these simple downlinks can be easily fed into the Internet for live worldwide distribution of data. These designs are all based on the amateur radio standard on-air AX.25 packet network protocol that is implemented in a number of off-the-shelf modems (called Terminal Node Controllers or TNC’s). The following paragraphs describe three such hardware devices and the remainder of this paper describes how TNC’s and the AX.25 protocol were used on PCsat. STARSHINE’s. Here are our OFF-THE-SHELF AX.25 HARDWARE choices for AX.25 hardware: One advantage of using the AX.25 The MIM Module protocol is that any node in the system can be used for relaying The simplest Telemetry module is data between any other nodes. the one cubic inch MIM module Thus, the TNC can not only which provides for multiple provide the dedicated up and periodic AX.25 packets at 1200 downlinks and command/control baud AFSK containing up to 5 channels, but also serve as a analog channels and 8 on/off generic relay for other bits. Different rates can be set applications on a secondary for the BEACON, Telemetry, GPS basis. Examples of TNC’s on position and CW Identification. orbit are SAREX, SPRE, MIR, ISS, The module has no command and SUNSAT, OPAL and soon to be control capability, but that is PCsat, SAPPHIRE and maybe future easily added with CTCSS or DTMF receivers/decoders. Bob Bruninga 15th Annual AIAA/USU Conference on Small Satellites SSC01-VIIIb-1 The 9612+ TNC adds a second comm. Port to the TNC offering one port at 1200 and the other at 9600 baud. The 9612+ offers the same 5 analog telemetry channels of the MIM module and serial port communications of other TNCs, but also gains a total of 8 configurable command or I/O bits, four ON/OFF command bits and one input bit. Because of the added 9600 baud comm. Port, the KPC- 9612+ TNC was designed into the final PCsat design. PCsat is Photo 1. The MIM module. See just one of a possible http://www.toad.net/~wclement/bru constellation of student built ninga/mic-lite.html satellites supporting the ASTARS Mission all based on using AX.25 TNC’s in orbit. 1200 Baud KPC-3+ The second and more capable THE ASTARS MISSION telemetry is the use of a Kantronics KPC-3PLUS TNC which The ASTARS Mission is a generic has the advantage of an AX.25 mission (supported by any TNC in receiver and thus the ability to orbit) to provide real-time do command and control. It can message, position, and status even be carved down to fit within relay via satellite to a the four inch cube. The board worldwide Internet linked amateur will fit diagonally in a Cubesat radio tracking system. Any if the connectors are removed amateur or university payload can and the power supply portion of support this mission by simply the board is relocated enabling the DIGIPEAT-ON function in any AX.25 compatible transponder (TNC). The users of such a relay system can be for Boats at Sea, remote environmental sensors, cross country travelers, expeditions, school projects, or any other travelers which are far from any existing APRS terrestrial tracking infrastructure. The satellite downlink from such travelers or remote sites are fed into the existing worldwide Internet linked ground system by a few permanent ground stations. This gives the same Telemetry, These APRS satellites would join Beacon, GPS and CW ID capability our own PCsat, and other as with the MIM module, but University built small satellites includes a full TNC DIGIPEATER to provide connectivity to and 4 channel COMMAND/CONTROL everyone involved in this mission channel as well. With the full providing connectivity to their TNC, a complete digital birds while not locally in view.. communications transponder mission, such as used on PCSAT, The Space segment of PCsat/ASTARS can be supported. has been demonstrated a number of 9600 Baud KPC-9612+ times in space via MIR School Bob Bruninga 15th Annual AIAA/USU Conference on Small Satellites SSC01-VIIIb-1 tests, the Shuttle SAREX, the for worldwide real-time message SPRE mission, AO-16, UO-22 and and position/status data exchange more recently via SUNSAT and ISS. between users and is in contrast The satellite concepts described to the mission and design of all herein would be operated under existing amateur PACSATS that the rules of the Amateur concentrate on message store-and- Satellite Service and the rules forward. Further, it of the FCC. Full details of the incorporates the Internet as part Cubesat concepts and the PCsat of its design instead of trying mission can be found at: to compete with it. Although the Naval Academy has been in dialog http://web.usna.navy.mil/~bruning with a number of other satellite a/cubesat.html owners and designers over the http://web.usna.navy.mil/~bruning last 7 years to accommodate these a/astars.html concepts into their designs as well (SAREX, SPRE, MIR, ASUsat, UO-22, and SUNSAT), PCsat will be the first satellite designed with APRS UI digipeating as the primary mission with these objectives: 1) Handheld/Mobile live digital tracking and communications in footprint 2) Worldwide handheld and mobile position and status reporting (via internet) 3) Handheld and Mobile message uplink to satellite (then to Internet) 4) Handheld and Mobile message downlink/delivery from Internet 5) Nationwide Bulletin delivery Photo 2. Personal Communications 6) Low Power GPS tracking of buoys, Satellite (PCsat) with Antennas telemetry devices, wildlife, etc 7) Other UI digipeating applications 8) Worldwide one-line Emailing 9) School demonstrations and satellite lab activities All of these mission objectives can be met with just a simple hardware TNC on orbit acting as a UI digipeater. Also, with the sophistication and added I/O of recent TNC’s designed for APRS, the TNC itself can be the command and control system. Thus no additional on-orbit CPU’s are required. Not only is the satellite hardware simple, but it can be reproduced by other satellite builders to help form a Photo 3. Personal Communications constellation of these relay Satellite, PCsat and Design Team satellites, all operating on the same frequency to give mobile The PCsat MISSION users extended access beyond what is possible with one satellite The remainder of this paper will alone. This concept of a describe the design of a low cost Builders Channel for similar- easy to build APRS satellite to mission spacecraft was presented meet the need for mobile and at last years AMSAT Symposium handheld amateur satellite users. [1]. This APRS Satellite Mission is Bob Bruninga 15th Annual AIAA/USU Conference on Small Satellites SSC01-VIIIb-1 BACKGROUND TO THE MOBILE SATELLITE NEED Modern Technology is on the move. Satellite Wireless is the leading edge of technology. In the amateur satellite program, it should be a major driver for future amateur satellite missions. In just the last year there have been many hints at the future of Amateur Mobile and Handheld satellite communications. Photo 4. Chas Richard, W4HFZ’s 1) Growing popularity of UI mobile APRS Satellite capability digipeating via MIR through (including HF). With an APRS 1999 2) Continuing high popularity of Satellite, he can send and AO27 for handheld FM voice receive brief text messages communications. anywhere on the planet a few 3) Activation of UO-14 for FM times a day. voice repeater mode in February 2000 4) Experimental UI digipeating ASTARS via the UO-22 Satellite 5) FM VOICE repeating via SUNSAT To identify this APRS satellite SO-35 throughout 1999 6) Recent activation of SUNSAT communications system from its SO-35 for UI and APRS terrestrial counterpart the space 7) Recent Introduction of new segment is called ASTARS for APRS TNC/Radios (Kenwood & Alinco) Satellite Tracking and Reporting 8) Dayton 2000 introduction of System which has evolved through the upgraded Kenwood TH-D7 a number of existing and previous data HT! satellite communications experiments. First was 1200 Baud The potential of two-way PSK ASTARS which was called satellite handheld text messaging TRAKNET [2] at the 1998 and 99 (national paging) was AMSAT conferences using AO-16, serendipitously demonstrated at LO-19 and IO-26. It is a very the Dayton Hamvention during a viable capability for stations parking lot demo of the SUNSAT with PSK TNC's or using more downlink.